Organic electronics is an important area for commercial development including, for example, advanced transistors, displays, lighting, photovoltaic, and sensing devices. The broad diversity of organic compounds and materials provides advantages for organic electronics. In but one example of the versatile chemistry and material science available for organic electronics, tetracarboxylic diimide derivatives of rylenes, particularly of napthalene and perylene (NDIs and PDIs, respectively), represent one of the most extensively studied classes of functional materials in the field of organic electronics. The thermal, chemical, and photochemical stability as well as their high electron affinities and charge-carrier mobilities render these materials attractive for applications in organic field-effect transistors (OFETs) and organic photovoltaic cells (OPVs). They have also been widely used as acceptors in transient absorption studies of photoinduced electron-transfer, again due to their redox potentials, and to the stability and distinctive absorption spectra of the corresponding radical anions.
The N,N′-substituents of PDIs and NDIs generally only have minimal influence on the optical and electronic properties of isolated molecules, although they can be used to control solubility, aggregation, and intermolecular packing in the solid-state. In contrast, core substitution of these species typically has a much more significant effect on the redox potentials (enabling, in some cases, the electron affinities to be brought within a range in which air-stable OFET operation can be achieved) and optical spectra of these species. Moreover, core substitution can be used as a means of constructing more elaborate architectures such as conjugated oligomers or polymers and donor or acceptor functionalized products.
Functionalized NDIs are most effectively obtained through the selective bromination of naphthalene-1,4:5,8-tetracarboxylic dianhydride (NDA) with dibromoisocyanuric acid (DBI) in concentrated sulfuric acid or oleum, followed by imidization with the primary amine of choice in refluxing acetic acid. NDA can also be brominated using Br2 in concentrated sulfuric acid or oleum. The brominated NDI can then serve as an intermediate for further functionalization through either nucleophilic substitution to afford amino, thiol or alkoxy substituted derivatives, or through palladium-catalyzed coupling reactions to yield cyano, phenyl, alkynyl and thienyl functionalized products. However, the range of conjugated species that can be obtained by palladium-catalyzed methods is determined by the availability of appropriate candidate coupling partners. In particular, metallated reagents such as stannanes can be difficult to obtain for electron-poor (acceptor) building blocks.
Additionally, monobrominated NDI, which is useful for a full range of NDI derived compounds, generally can only be obtained by manipulating the equivalents of brominating reagents and/or by manipulating reaction conditions; however, a difficult to separate mixture of non-brominated, monobrominated, and dibrominated results, which makes large scale production impractical.
Accordingly, both mono- and di-metallated NDI species would be valuable building blocks for new types of conjugated NDI derivatives in which acceptor groups are directly conjugated to the NDI core.